1. Field of the Invention
The present invention relates to a wireless independent network based on carrier sense multiplexing access (CSMA)/collision avoidance (CA). More particularly, the present invention relates to a method for sharing hybrid resources in a wireless independent network, a station for the method, and a data format for the method and the station.
2. Description of the Related Art
Wireless independent networks connect wireless stations without the use of wires in a predetermined area regardless of connections to base networks. For example, home networks connecting information regarding home electronics without the use of wires is a type of wireless independent network. Services in a wireless independent network may generally be classified into a real-time Audio Video (AV) streaming service or a non-real-time AV streaming service.
An environment of such a wireless independent network may be characterized as follows. First, since network subscribers' interests concentrate on a real-time AV streaming service in one independent network, it is rare for a large number of real-time AV services to coexist in one independent network. Second, a small number of real-time AV streaming services and a large number of non-real-time AV streaming services can coexist in one independent network. Third, the real-time AV streaming service uses a station that is the subject thereof and limited holding time exists in the service.
In the above-described wireless independent network environment, wireless stations (STAs) typically share wireless communications resources. Here, a conventional resource-sharing method may generally be classified into a distributed coordination method or a centralized control method.
The distributed coordination method uses a mechanism for minimizing possible message collisions that occur when stations attempt to use a data channel simultaneously. This mechanism is the IEEE 802.11a distributed coordination function (DCF) based on CSMA/CA. In a distributed coordination method using a DCF, random backoff numbers are created to minimize competition-based collisions, the backoff numbers are reduced by stages when a channel is idle for at least a predetermined period of time (in the case of IEEE 802.11, this is referred to as DCF Interframe Space (DIFS)), and data is transmitted when the backoff number becomes “0”. A conventional distributed coordination method for grading priorities of the occupation of resources according to a specific type of data includes a Point Coordination Function (PCF) Interframe Space (PIFS) system and a Short lnterframe Space (SIFS). Priorities of these systems are in the relationship DIFS>PIFS>SIFS, and a station using SIFS has priority over a station using DIFS. However, since a DCF system works on a probabilistic base, it is still possible for stations to collide.
In the centralized control method, one control station controls resources shared in a wireless independent network in a bundle. Thus, wireless stations share wireless resources according to the instructions of the control station. The centralized control method may be subdivided into a direct mode and an indirect mode. In the direct mode, a control station controls the time slots for transmission and reception among wireless stations so that the wireless stations directly communicate with one another. The HiperLAN/2 standard is a representative example of the direct mode. In the indirect mode, transmission data of all stations is transmitted to the control station so that the wireless stations indirectly communicate with one another through the control station. This indirect mode is based on the Bluetooth standard.
Accordingly, in the above-described distributed coordination method, a specific control station is not required, and a mesh network can be constituted, and a station may easily subscribe to and withdraw from the mesh network. However, the distributed coordination method uses resources ineffectively and cannot support the real-time AV streaming service. In addition, the centralized control method in the indirect mode cannot support the real-time AV streaming service due to the forwarding of packets, which concentrates loading on the control station, and requires the selection of a substitute node when the control station withdraws from the subscribed network. Although the centralized control method in the direct mode uses resources effectively, supports the real-time AV streaming service, and constitutes the mesh network, loading is concentrated on the control station, thus requiring the selection of a substitute node when the control station withdraws from the subscribed network.
The aforementioned conventional resource-sharing methods have many problems since they have been developed based on non-real-time services, or due to inflexible structure of networks.